Beneficiation of vanadium-containing materials

ABSTRACT

A process for the beneficiation of vanadium-containing materials comprising preheating the material in the absence of oxygen and then reacting the hot material with oxygen to yield soluble vanadium compounds. This Application for a patent is a continuation-in-part of my earlier U.S. Pat. application Ser. No. 755,431 filed on Aug. 26, 1968, and now abandoned.

United States Patent [191 Vojkovic [451 Aug. 21, 1973 BENEFICIATION OFVANADIUM-CONTAINING MATERIALS [75] Inventor: Milos Vojkovic, Luxembourg,

211 App]. No.: 77,315

Related US. Application Data [63] Continuation-impart of Ser. No.755,431, Aug. 26,

1968, abandoned.

[52] U.S. Cl 75/1, 75/24, 75/84 [51] Int. Cl...... C22b l/00, C221:7/04, C22b 55/00 [58] Field of Search 75/1, 21, 24, 84, 75/27, 29, 63,96, 3, 7,59

[56] References Cited UNITED STATES PATENTS 1,970,467 8/1934 Mayr 75/273,163,523 12/1964 Porter 75/65 2,242,759 5/1941 Schlecht 75/84 3,425,8262/1969 Schmidt 75/84 3,305,355 2/1967 Darrow 75/1 2,369,349 2/1945Hatherell 75/1 3,428,427 2/1969 Raicevic 75/1 3,118,757 1/1964 Peras75/1 2,867,529 1/1959 Forward 75/7 2,864,689 12/1958 Perrin 75/593,295,952 1/1967 Johnson 75/3 2,867,529 1/1959 Carpenter 75/7 FOREIGNPATENTS OR APPLICATIONS 127,026 0/1960 U.S.S.R 75/24 Primary Examiner-L.Dewayne Rutledge Assistant Examiner-Peter D. Rosenberg Attorney-C. R.Hoffman, G. Levy, D. S. Kane, .1. C. Sullivan, J. T. Salerno, Jr., C. P.Bauer, D. H. Kane, P. T. Dalsimer, J. Kurucz, M. E. Goldstein, P. Saxonand P. C. Van Der Sluys [5 7] ABSTRACT A process for the beneficiationof vanadium-containing materials comprising preheating the material inthe absence of oxygen and then reacting the hot material with oxygen toyield soluble vanadium compounds.

13 Claims, No Drawings BENEFICIATION F VANADlUM-CONTAINING MATERIALSThis Application for a patent is a continuation-inpart of my earlier US.Pat. application Ser. No. 755,431 filed on Aug. 26, 1968, and nowabandoned. This invention relates to the beneficiation ofvanadium-containing material, the vanadium component of which can beoxidised to form soluble vanadium compounds.

There are no known naturally occurring materials that are rich invanadium, and the metal is commonly obtained as a by-product in theproduction of other metals. In particular, it is known to obtainvanadium from slags (that is to say, solid materials that separate fromthe main, liquid component during smelting operations) obtained by thesmelting of ores, especially slags formed in the manufacture of steel.In such slags, the vanadium is in a complex form in a spinel-typestructure and is thus largely or completely in the trivalent state.

Vanadium can be extracted from such slags by oxidising the vanadium tothe pentavalent state in the presence of salts of alkali metals. Thisbreaks up the spinel-type structure and leads to the formation ofsoluble vanadates, which can be leached out in a conventional manner.

The oxidation of such slags for this purpose, however, presents a numberof difficulties. First, the slag granules become coated with an oxidelayer that inhibits further reaction and thus necessitates a longretention time for the slag in the reactor (so that the throughput/sizeratio is low) and results in a low thermal efficiency. Further, both thetemperature and the concentration of salts of alkali and/or alkalineearth metals have to be carefully controlled if the slag is not tosoften and adhere to the walls of the reactor.

This invention provides a process for the beneficiation ofvanadium-containing material, the vanadium component of which can beoxidised to form vanadium compounds that are soluble in an aqueousmedium, which comprises preheating the material under inert conditionsand then contacting the resulting hot material with oxygen to effect theformation of soluble vanadium compounds, the temperature of thepreheated material when it is initially contacted with oxygen being suchthat the material reacts with the oxygen in a strongly exothermicmanner.

When the vanadium-containing material is vanadium-containing slag, theprocess comprises preheating the slag in particular form under inertconditions and then contacting the resulting hot slag with oxygen toeffect the formation of soluble vanadium compounds, the temperature ofthe preheated slag when it is initially contacted with oxygen being atleast 600 C and such that the slag reacts with the oxygen in a stronglyexothermic manner, and the maximum temperature reached by the slag whileit is in contact with the oxygen being within the range of from 680 C.to l,050 C.

For vanadium-containing materials other than vanadium-containing slag,the process comprises preheating the material under inert conditions andthen contacting the resulting hot material with oxygen to effect theformation of soluble vanadium compounds, the temperature of thepreheated material when it is initially contacted with oxygen being atleast 400 C and such that the material reacts with oxygen in a stronglyexothermic manner, and the maximum temperature reached by the materialwhile it is in contact with the oxygen being within the range of from600 C. to l,200 C.

With the process of the invention, it is possible to reduce considerablythe reaction period of vanadiumcontaining material with oxygen and atthe same time to increase the percentage extraction of the vanadiumcomponent of the material over that obtained by the conventionalextraction processes used with such materials. The throughput/size ratioof the plant in which the process is performed can be increased and thematerial can be oxidised in smaller batches allowing easier temperaturecontrol.

The process of the invention can be used irrespective of the vanadiumcontent of the starting material. Further, the process of the inventionmakes it practicable to extract vanadium from materials from whichextraction 'was previously impracticable for economic reasons. Of thematerials other than slags, the process of the invention is especiallyimportant when the starting material is titaniferous ore, for example,titaniferous magnetite or fly ash, which is a product of crude oilcombustion, or ferrophosphorus.

The temperature to which the material is preheated should besufficiently high to ensure that, when the material is contacted withoxygen, the material reacts rapidly with the oxygen in a stronglyexothermic manner. Thus, if the preheat temperature is sufficientlyhigh, the temperature of the material will rise sharply, usuallyby atleast 50 C. and advantageously by at least C., when it is contacted withoxygen. The minimum satisfactory preheat temperature for a particularmaterial can only bedetermined by trial and error but it depends uponthe chemical composition and degree of physical sudivision of thematerial (the minimum satisfactory preheat temperature decreasing as thedegree of the physical subdivision of the material becomes finer) thepresence of any additives and the chemical composition and theconcentration of the additives, if any.

Depending on the above mentioned factors, it will generally be foundadvantageous to preheat, for example, vanadium-containing titaniferousores to a temper ature within the range of from 800 to l,000 C. and,preferably, within the range of from 850 to 950 C. Fly ash isadvantageously preheated to a temperature within the range of from 400to 750 C.

With regard to the chemical composition of vanadium-containing slags,there is a broad distinction between, on the one hand, slags that have arelatively high vanadium content (say, at least 10 percent by weightcalculated as V 0 and based on the total weight of the slag and, on theother hand, slags that have a relatively low vanadium content and a highcontent of calcium and/or magnesium, and possibly a substantial contentof titanium. The slags in the first of these two broad categories, thatis to say, those that have a relatively high vanadium content, normallyhave incorporated with them'prior to roasting (as is described ingreater detail hereinafter) a salt or salts of an alkali metal to serveas a fluxing agent, and require a relatively low pre-heat temperature.The slags in the second of these categories, on the other hand, requirea relatively high preheat temperature. Also, it has been found that theminimum satisfactory preheat temperature is a decreasing function of thequantity Fe Si/Ca Mg where Fe, Si, Ca and Mg stand for the proportionsby weight of these elements in the slag.

The minimum satisfactory preheat temperature decreases as the degree ofphysical subdivision of the slag becomes finer. Thus, for example, itwas found that a batch of slag required a preheat temperature of 850 C.when ground to pass a 44 mesh (B.S.S.) screen, which corresponds to amaximum particle diameter of approximately 350 microns, whereas apreheat temperature of 750 C. sufficed when slag from the same batch wasground to pass a 200 mesh (B.S.S.) screen, which corresponds to amaximum particle diameter of approximately 75 microns.

It is usually advantageous to preheat slag to a temperature of at least630 C., and it will generally be found preferable not to preheat it to atemperature exceeding 800 C.

The requirement that the material should be preheated under inertcondition implies primarily that it should be preheated in the absenceof oxygen. The purpose of preheating the material is simply to ensurethat it is at a desired elevated temperature when it is contacted withoxygen, and not to effect any chemical change in the material. Thus, inaddition to excluding oxygen, the material will be preheated in theabsence of any substance with which it would react to any substantialextent during the preheating.

The material may be preheated in an inert atmosphere, for example, anatmosphere of nitrogen, or it may be preheated while confined within aregion that is substantially completely filled by the material, and saidregion preferably being the interior of a conduit through which thematerial is supplied to a zone wherein it is contacted with the oxygen.The feasibility of preheating slag in a conduit that communicates withthe oxidation zone arises in part from the fact that, during preheating,vanadium-containing slags evolve some water vapour and also, in the caseof basic slags, a mixture of carbon monoxide and carbon dioxide, and inpart from the fact that it is possible to feed the slag through theconduit in the form of a relatively tightly packed plug.

The material is advantageously preheated by means of radiant heaters,but, when the material is preheated in an atmosphere of an inert gas, itmay be preheated by heating the gas and fluidising or agitating a bed ofmaterial in particular form by passing the hot inert gas upwardlythrough it.

Since the purpose of preheating the material is that the material shouldbe hot when it is contacted with oxygen, care should naturally be takento prevent any substantial cooling of the material after it has beenpreheated and before it is contacted with oxygen.

The preheated material is advantageously contacted with substantiallypure oxygen, but, if it is found that this results in the materialreaching too high a temperature, the oxygen may be diluted with an inertgas. Thus, the preheated material may be contacted with oxygen-,enriched air or even with air. The use of air, however, will usuallyresult in the maximum temperature reached by the material being too lowunless the air is also preheated. Further, it may be found that, inorder to supply oxygen at the rate required for the reaction, the rateof supply of air has to be so high as to cause dusting losses.

The oxidation reaction that takes place when the preheated material iscontacted with oxygen is exothermic and the maximum temperature reachedby the material depends upon therate of reaction (which in turn dependsupon the concentration of the oxygen, the rate of diffusion of theoxygen to the material, the composition of the material including anyadditives, and the fineness of the particles of the material), on therate of loss of heat from the reaction mixture, and on the temperatureto which the material is preheated. Thus, there are a number ofdifferent parameters that can be controlled to ensure that the materialremains within the desired temperature range during the oxidationreaction.

The maximum temperature reached by the material while it is in contactwith the oxygen should not be so high that there is formed such a largeliquid-phase component that the extraction efficiency is seriouslyreduced. Also, the said maximum temperature should not be so high thatexcessive sintering of the material occurs. As a rough guide, anysintering of the material should not be sufficiently severe to preventthe material after quenching, from being crumbled. It may be added thatthe maximum temperature reached by the material while it is in contactwith the oxygen is always substantially below the temperature at whichvanadium metal becomes incandescent.

in the case of slag, in general, and especially when (as is describedhereinafter) a salt or salts of an alkali metal or metals is or areincorporated with the slag prior to its being contacted with oxygen, themaximum temperature reached by the slag while it is in contact with theoxygen advantageously does not exceed 840 C. and preferably does notexceed 820 C., because there is a tendency for a serious reduction inextraction efficiency to occur if the temperature is allowed to risesufficiently high for alkali vanadates for other alkali or alkalineearth salts to fuse. Fortunately, however, those slags that require ahigh preheat temperature, say, over 800 C., are also relativelyrefractory, that is to say, they can be allowed to reach a relativelyhigh temperature while in contact with oxygen, but it will generally befound advantageous not to allow the temperature of the slag to exceed950 C. while it is in contact with the oxygen.

When (as is described hereinafter) oxidised slag is subsequently treatedby leaching with acid, it is found that the quantity of acid required toextract a given quantity of soluble vanadium decreases as the maximumtemperature reached by the slag while in contact with the oxygenincreases. Thus, if the maximum temperature reached by the slag while incontact with the oxygen slightly exceeds the temperature, or the upperend of the temperature range, that gives the maximum oxidation of thevanadium component, the decreased consumption of acid in the subsequentleaching stage will tend to offset the economic disadvantage of thelower oxidation of the vanadium component. Also, the improved oxidationof constituents of the slag other than the vanadium component thatresults from operating with a higher maximum temperature of the slagwhile it is in contact with the oxygen prevents or lessens the loss ofvanadium through reduction during the sub sequent extraction stages.Indeed, it may in some cases be economically advantageous to operate inthis way at a slightly lower extent of oxidation of the vanadiumcomponent, because it is possible, in economic terms,

for the lower oxidation of the vanadium component to be more than offsetby the resulting lower acid consumption and the avoidance or lesseningof vanadium reduction during the extraction stages.

At least when the preheated slag is contacted with substantially pureoxygen, it will usually be found that the preferred upper limit of 820C. (referred to hereinbefore) for the maximum temperature reached bycertain slags during the oxidation reaction implies an upper limit of680 C. for the temperature to which the slag is preheated.

Grinding the material more finely improves the extraction efficiency,but against this there has to be offset the greater cost of finergrinding. For a given extraction efficiency, finer grinding generallyenables the preheating temperature and/or the exposure time to oxygen tobe correspondingly reduced. Slag is advantageously ground to 36 mesh(8.8.8.), which corresponds to a maximum particle diameter ofapproximately 420 microns, and it may be ground to as fine as 85 mesh(3.8.8.), which corresponds to a maximum particle diameter ofapproximately 175 microns, or even finer if desired. Other materials areadvantageously ground to 100 mesh (3.5.8.) or even finer. When thematerial is titaniferous ore, it is advantageously ground to as fine as200 mesh (8.8.5.) or -400 mesh (B.S.S.).

Advantageously, a salt of an alkali metal, or a mixture of more than oneof such salts, preferably, sodium chloride or sodium carbonate or amixture of sodium and potassium chlorides, or a mixture of sodiumchloride and sodium sulphate, is incorporated with the material prior toits oxidation. The salts serve as fluxing agents and their additionimproves the yield of soluble vanadium by providing cat-ions for theformation of alakali vanadates. Because the salt or mixture of saltsundergoes an endothermic reaction when the oxidation takes place, theaddition of such salts provides a further method of achieving thedesired temperature control. In the case of sodium carbonate, theliberation of carbon dioxide tends further to reduce the rate of thereaction, so that the incorporation of sodium carbonate with thematerial before it is contacted with the oxygen can provide a verysubstantial degree of temperature control. Y

The selection of the salt or mixture of salts to be added for theoptimum results depends upon the chemical composition of the material.It will generally be found that the salt or mixture of salts to be addedshould be one which forms sodium oxide readily on exposure to oxygen.Advantageously, when titaniferous ore or fly ash is used as the startingmaterial, the salt of an alkali metal incorporated with the material issodium carbonate.

The quantity of the selected salt or salts to be added will depend onthe proportion of alkali metals or alkaline earth metals present in thematerial originally, a smaller addition (or no addition) being requiredif the original content is higher. In general with slags, it will befound that the addition of such salts is most beneficial whenincorporated with slags that have a relatively high vanadium content.

Preferably, the quantity of sodium carbonate incorporated intitaniferous ore is such that it comprises at least l percent of thetotal weight of the material and the quantity of sodium carbonateincorporated in fly ash is such that it comprises at least 25 percent ofthe total weight of the material.

In addition to, or instead of, the incorporation of a salt or a mixtureof salts, to obtain the desired temperature control it may be foundadvantageous in the extraction of vanadium from some materials toincorporate with the material prior to its oxidation one or more othervanadium-containing materials, the vanadium component of which can beoxidised to form vanadium compounds that are soluble in an aqueousmedium, of differing chemical composition. For example, the startingmaterial may comprise a mixture of vanadiumcontaining slag and anothermaterial. If the material to be oxidised reacts violently on exposure tooxygen it is preferably mixed with a material that reacts slowly onexposure to oxygen. This can result in the average percentage ofvanadium extracted from the roasted mixture after oxidation beingincreased over the percentage extraction obtained when each of thematerials is roasted separately. For example, ferrophosphorus isadvantageously mixed with a basic vanadium containing slag.

With some materials it may be found, after roasting in accordance withthe invention (primary roasting), advantageous to perform a secondaryroasting operation, the material being ground or otherwise comminutedbetween the primary and secondary roasting operations. If the materialis allowed to cool after the primary roasting operation, it may eitherbe preheated again under inert conditions before being contacted at anelevated temperature with oxygen for a second time or the-secondaryroasting operation may be carried out in a conventional manner. Thissecondary roasting generally increases the average extraction ofvanadium for a given starting material and enables more reliable andconsistent results to be obtained. The salt of an alkali metal ormixture of salts and/or the one or more other vanadium-containingmaterials may be added at the primary roasting stage or at the secondaryroasting stage or at both stages.

When ferrophosphorus is used as the starting material, it isadvantageously roasted in accordance with the invention in the absenceof additives, ground, mixed with basic vanadium-containing slag, and,preferably, also with sodium carbonate, and re-roasted by againpreheating under inert conditions and contacting it at an elevatedtemperatre with oxygen.

After roasting, the material is advantageously quenched. It may then betreated, for example, in a conventional manner, to yield vanadium oxide.As compared with allowing the material to cool slowly, quenching gives asmall improvement in extraction efficiency.

The liquid medium in which the vanadium compounds, that are formed as aresult of the process of the invention, are soluble may be water, or analkali medium, or an acid medium. it will generally be found that thevanadium compounds are soluble in water or an alkali medium but it mayin some cases be necessary to use an acid medium.

In the case of slags that are rich in vanadium (for example, containingfrom 8 to 15 percent by weight of vanadium based on the total weight ofthe slag, corresponding to from approximately 14.3 to 26.8 percent ofvanadium calculated as V 0 and free from phosphorus and to which sodiumcarbonate has been added before roasting, the hot slag that has beencontacted with oxygen may be quenched with water, wet-milled and hotdigested. After filtering, the strongly alkaline filtrate is neutralisedto precipitate dissolved silica which is coagulated with a flocculatingagent and removed by filtering. The silica-free liquor is then eithertreated to give ammonium metavanadate by direct salting with ammoniumchloride at a pH of about 7 or treated to precipitate a hydrated acidpolyvanadate. The metavanadate or polyvanadate is decomposed thermallyto give flake of vanadium pentoxide.

In the case of slags that have a low vanadium content (for example,containing less than 10 percent by weight of vanadium calculated as Vand based on the total weight of the slag and that contain phosphorus,the hot slag that has been contacted with oxygen may be quenched withwater, wet-milled, and then leached with dilute acid, for example,dilute sulphuric acid, or quenched and leached with a dilute acid. Thedilute acid is suitably added until a steady pH of 1 is reached at 50 C.The impure liquor may then be treated, for example, by passing gaseouschlorine through the liquor until an e.m.f. of -750 mV is reached, toensure that any iron present is oxidised and the liquor is thensubjected to a solvent-extraction process that extracts vanadiumpreferentially, the solvent used in the extraction being an organicliquid, which may comprise a tertiary amine in admixture with one ormore organic solvents. The organic phase obtained in the extraction isstripped of vanadium by the use, for example, of an aqueous solution ofsodium carbonate, and recycled for futher use. The vanadium is obtainedas ammonium metavanadate by treating the sodium vanadate solution withammonium sulphate. Alternatively, ammonium metavanadate may be obtainedwithout the use of sodium carbonate by adding ammonium chloride directlyto the organic phase containing the vanadium. In each case the productis heated to give fused vanadium pentoxide flake.

The process is advantageously carried out continuously, a mass of thematerial being carried in turn through a preheating zone and anoxidation zone. After leaving the oxidation zone, the materialis'preferably carried to a quenching zone. When it is desired to performa two-stage roasting process, the mass of material, after leaving theoxidation zone, is preferably carried through a grinding zone, whereaggregates are mechanically broken down, to a further preheating zoneand a further oxidation zone before being carried through the quenchingzone. The material is preferably carried, at least through the oxidationzone or zones, in the form of a shallow static bed supported on aconveyor, which may be a rotary hearth or a moving belt or grate. Whenthe starting material is slag, the depth of the bed is preferably withinthe range of from 1 to centimetres.

Several series of experiments were carried out with different startingmaterials to compare the process of the invention with the conventionalmethod and to investigate the effects of different inert atmospheres forthe preheating, and changes in preheating temperature, the rate ofdiffusion of oxygen to the preheated charge, length of time of exposureto oxygen, particle size, layer thickness of the charge, oxygenconcentration, and the addition of other substances as well as theeffects of secondary roasting on the extraction of vanadium from thematerial.

An experiment was carried out to investigate, whether the nature of theinert atmosphere (the term inert atmosphere" being used throughout thespecification to denote an atmosphere that does not undergo anysubstantial chemical reaction with the material during the preheating)in which the material is preheated afi'ects the extent to which thematerial is oxidised when it is contacted with oxygen. Thus, samples ofthe same batch of slag were preheated to the same temperature inatmospheres that consisted, respectively, (to the extent of more than 99percent by volume in each case) of nitrogen, helium, carbon dioxide anda mixture of nitrogen, carbon dioxide and steam. The preheat temperatureand all other relevant conditions were maintained the same and it wasfound that, to within the limits of experimental error, the extent ofoxidation of the slag that is to say, the change in weight of the slagas a result of the oxidation step, was the same in each case. On theother hand, when, contrary to the invention, further samples from thesame batch of slag were preheated to the same temperature in anatmosphere that contained an appreciable proportion of oxygen, all otherrelevant conditions being maintained the same as before, it was foundthat the extent of oxidation of the hot slag was materially reduced.Thus, taking the extent of oxidation when the slag was preheated in aninert atmosphere as being 100 percent, it was found that the presence ofl 1 percent by volume of oxygen in the atmosphere in which the slag waspreheated reduced the extent of oxidation to 68.8 percent, while 20percent by volume of oxygen reduced the extent of oxidation to 45.0percent and 33 percent by volume of oxygen reduced it to 17.1 percent,the balance being nitrogen in each case.

A series of experiments was performed with, as the starting material,vanadium-containing titaniferous magnetite a chemical analysis of whichore revealed that its composition was as follows, the percentages beingby weight based on the total weight of the material:

Fe O 62.3% TiO, 13.3% C50,, 1.16% SiO 7.52% MnO 0.37% v,o. 1.79%

The ore, which was in the form of lumps of up to 3 inches in diameter,was crushed by passing through a 4 inch jawcrusher to reduce the size ofthe lumps to one-fourth inch in diameter and under. The ore was thenreduced in size further either by a dry ballmill until the particles allpassed through 60 mesh (B.S.S.) screen or by a shatter box using asingle pass and a residence time of 3 minutes to reduce the size of theparticles to less than microns.

The ore that had been ground in the shatter box was blended with sodiumchloride until the proportion of sodium chloride in the mixture was 28.6percent by weight based on the total weight of the mixture. A sample ofthis charge was then roasted, not in accordance with the invention, at800 C. in an electrically heated muffle furnace in a conventionalmanner. It was found that the percentage by weight of the total vanadiumcontent of the charge extracted from the charge after it had beenroasted for 1 hour was 44.4 percent and after 2 hours was 47.3 percent.

A further sample of the same charge was then roasted in accordance withthe invention and the percentage by weight of vanadium extracted basedon the total vanadium content of the charge was measured for differentinert preheating temperatures and, in each case, an exposure time tooxygen of 10 minutes. It was found that the percentage vanadiumextraction for a preheating temperature of 700 C. was 37.3 percent butthat this rose to 59.7 percent for a preheating temperature of 800 C.Thus, when the charge was preheated to 800 C. in an inert atmospherebefore exposure to oxygen for 10 minutes the percentage vanadiumextraction obtained was greater than that obtained by roasting thecharge at 800 C. for 2 hours in the conventional manner.

The ground titaniferous magnetite was blended with sodium carbonateuntil the proportion of sodium carbonate in the mixture was 28.6 percentby weight based on the total weight of the mixture and the experimentswere repeated. For conventional roasting at 800 C. the percentagevanadium extraction after a roasting time of 1 hour was 77.0 percent byweight and this rose to 82.2 percent by weight after 2 hours. When thesame charge was roasted in accordance with the invention the resultsshown in Table I were obtained.

TABLE 1 Preheating temp. Length of period Percentage in C. of exposureto Vanadium oxygen, in minutes Extraction 600 10 34.0 700 10 81.2 800 1094.7 850 10 97.6

Thus, by using preheating temperatures above 700 C., the percentagevanadium extraction was increased over that obtained by using theconventional method with a much longer roasting period.

When titaniferous magnetite was preheated to a temperature of 600 C. ahigher percentage vanadium extraction was obtained when sodium chloridewas incorporated with the material prior to roasting than when sodiumcarbonate was used but, for preheating temperatures of 700 C. and above,considerably higher extraction percentages were obtained when sodiumcarbonate was incorporated with the material. The effects of theaddition of different materials on the extraction of vanadium are,however, described in more detail hereinafter.

To study the effect of different preheating temperatures on the recoveryof vanadium, the titaniferous magnetite that had been ground in theshatter box was blended with a quantity of sodium carbonate equal to23.05 percent by weight based on the total weight of the mixture.Samples of this charge in the form of layers of about 5 mm. in thicknessin small alumina boats were then preheated in an atmosphere of nitrogento different temperatures within the range of from 500 to l,050 C. andeach exposed to an atmosphere of pure oxygen for minutes. Each samplewas then wetmilled and digested in water at about 80 to 90 C. and thepercentage extraction of vanadium was calculated by measuring thequantities of soluble and insoluble vanadium present. The highproportion of sodium carbonate, the relatively long residence time inoxygen and the layer thickness were chosen so as to ensure that thepercentage recovery of vanadium did not depend sensitively upon theprecise values of these parameters. The results obtained are given inTable 11.

TABLE ll Preheating Temperature Percentage in C. Vanadium Extraction Forpreheating temperatures above 1,000 C. the formation of a liquid phaseduring exposure to oxygen caused the percentage vanadium extraction todecrease. lt is thought, however, that the residence time of the chargein the oxygen was too short for greater fusion of the charge, and hencethe formation of waterinsoluble or alkali-insoluble vanadium compounds,to take place. For preheating temperatures below 800 C. it is thoughtthat the formation of soluble vanadium compounds is caused by theeffects of exothermal heat given out when the preheated charge isexposed to oxygen.

A further series of experiments was carried out in which thetitaniferous magnetite that had been ground in the shatter box was mixedwith a quantity of sodium carbonate equal to 28.6 percent by weightbased on the total weight of the mixture. Samples of the charge werethen preheated in an inert atmosphere to different temperatures beforebeing exposed to pure oxygen for 10 minutes. The samples were onopen-ended trays in layers of 5 to 10 mm. in thickness which weresuspended horizontally so that they were in the middle of the path offlow of the oxygen. These measures were taken to increase the rate ofdiffusion of the oxygen to the charge. The results of the experimentsare shown in Table 111.

TABLE Ill Preheating Temperature Percentage in C. Vanadium ExtractionThus, as the rate of diffusion of oxygen to the charge is increased forthe same preheating temperature the vanadium extraction efficiency isalso increased.

Fly ash, recovered from flue gases in the burning of crude oil and inthe form of a dark brown powder, gave the results shown in Table IV whensubjected to a sieve analysis and the results shown in Table V whensubjected to a chemical analysis.

TABLE 1V Sieve Approximate Mesh Maximum Percentage Percentage (B.S.S.)Particle size of total Cumulative in microns weight weight +40 0.05 0.040+60 420 0.05 0.1 60+80 250 0.1 0.2 -+100 177 0.3 0.5 l00+l40 149 3.23.7 140+200 5.8 9.5 200+230 74 8.4 17.9 230+270 63 14.1 32.0 270+400 5310.8 42.8

TABLE V Percentage of total weight SiO, 14.94 Fe 2.80 Mn 0.09 P 0.067 A18.50 CH0 4.50 MgO 0.23 Cr 0 V 1.58 Cu 0 Ni 0.63 TiO, 1.18 Na O 0.29 K 00.50 C 55.70 S 2.60 Mo 0.04 Zn 0.05 Sr 0 Roasting the fly ash inaccordance with the invention in the absence of any additives proved tobe about 60% more efflcient in reducing the carbon content of the flyash than roasting in a conventional manner in a muffle furnace at 950 C.for a prolonged period. After reduction of the carbon content, achemical analysis of the fly ash was calculated on the basis of theanalysis obtained before roasting. This analysis is shown in Table VI.

TABLE V1 Percentage of total weight lS O, 33.65 6 6.32 Mn 0.20 P 0.15 A10 19.16 CaO 10.10 ga e 0.52 r 0 X 3.56 u 0 Ni 1.42 TiO 2.66 is C trace Strace Mo 0.09 Zn 0.10 Sr 0 A series of experiments was then carried outto investigate the effects of different inert preheating temperatureswhen using the fly ash as the starting material.

The fly ash was mixed with a quantity of anhydrous sodium carbonateequal to 28.6 percent by weight based on the total weight of the mixtureand samples were placed on metal plates, each sample being in a layer ofabout 1 cm. in thickness. The samples were then each preheated to adifferent temperature in an atmosphere of nitrogen which was thenreplaced by pure oxygen. After an interval of 5 minutes, each sample waseither rapidly withdrawn from the oxygen and quenched in water, theresults being shown in Table V11, or allowed to cool in nitrogen, brokendown and then re-roasted, the results being shown in Table V111. In thesecondary roasting process, each sample was preheated in inertatmosphere to the same temperature as in its primary roasting processand was again exposed to oxygen for 5 minutes.

TABLE V11 Preheating Temperature Time in Oxygen, Percentage in C. inminutes Extraction of Vanadium 500 5 87.0 525 5 91.5 550 5 91.9 575 589.0 600 5 90.7 625 5 93.3 650 5 90.5 700 5 87.7 750 5 82.8 800 5 73.3850 5 72.3

TABLE V111 Preheating Temperature Total Time in Percentage in bothprimary and Oxygen, in Extraction secondary roasting, minutes ofVanadium in C. after secondary roasting 300 10 12.14 400 10 92.70 450 1095.00 500 10 96.0 525 10 96.5 550 10 96.6 575 10 96.9 600 10 96.9 625 1097.1 650 10 96.9 675 10 97.3 700 10 97.3 725 10 96.85 750 10 95.60

When the results shown in Table V11 are compared with those in Table 11(noting that the preheating temperature of 300 C. is not within thescope of the invention), it will be seen that very much higher vanadiumextraction values for the same preheating temperatures and shorterperiods of exposure to oxygen are obtained for fly ash than fortitaniferous magnetite. It is thought that the presence of aconsiderable quantity of carbon dust by its combustion helped propagatethe oxidation reaction of the samples of fly ash preheated to only arelatively low temperature. Above preheating temperatures of 750 C.,considerable liquid-phase formation occurred and it is thought that thisaccounted for the reduction in the extraction of vanadium from samplesof fly ash preheated to these temperatures.

It will be seen from a comparison of the results obtained in Tables V11and V111 that the extraction of vanadium from fly ash is increased bysecondary roasting comprising preheating in an inert atmosphere andexposure to oxygen.

A further experiment was carried out in order to investigate the way inwhich the temperature of slag varied with time while it was in contactwith the oxygen after being preheated. Thus, a batch of slag containing7.01 percent V 0 3.82 percent P 0 41.80 percent Fe, 15.08 percent SiO1.66 percent A1 0 18.07 percent CaO and 6.14 percent MgO (thepercentages being by weight and based on the total weight of the slag)was ground to 200 mesh (B.S.S.), which corresponds to a maximum particlediameter of approximately microns, and a layer of the ground slag 1.25centimetres deep was preheated in an atmosphere of nitrogen to atemperature of 685 C. and then exposed to an atmosphere consistingsubstantially of oxygen. The temperature of the layer of slag wasmeasured, by means of a thermocouple buried in it, at intervals of 6seconds starting from when the preheated slag was first contacted withthe oxygen. The results, which are set out in Table 1X herein, suggestthat the rate of oxidation of the slag reached a maximum within thefirst 30 seconds.

TABLE lX Duration of exposure Slag temperature to oxygen in seconds C.685 6 705 I2 790 18 815 24 9l0 30 970 36 960 42 900 48 840 To study theeffects of different oxidation times on the extraction of vanadium, thetitaniferous magnetite, that had been reduced in size by the shatterbox, was blended with sodium carbonate until the proportion of sodiumcarbonate in the charge was 23.05 percent by weight. Samples of thematerial were then placed on open-ended trays, each sample being in alayer of about 10 mm. in thickness, and were preheated in an inertatmosphere to a temperature of 800 C. before being exposed to anatmosphere of oxygen, each sample being exposed for a different lengthof time. Each sample was then rapidly withdrawn and quenched in water.

The percentage vanadium extraction obtained after an exposure time of 10secs. was 80.3 percent by weight based on the total weight of thevanadium content of the charge sample and this rose to over 90 percentfor exposure times of from 20 secs. to 2 minutes. The oxidation reactionof the titaniferous magnetite is very fast, the charge being seen toglow on exposure to oxygen. This glow dies away very quickly.

Samples of the fly ash, blended with sodium carbonate in a proportionequal to 28.6 percent of the total weight of the mixture, were preheatedin an atmosphere of nitrogen to 650 C. and then exposed to oxygen fordifferent periods of time. The results obtained are shown in Table X.

TABLE X Time in oxygen, Percentage Vanadium in minutes Extraction 0 16.72.5 58.7 78.5 83.7 l5 91.7 95.9 30 96.5

When the roasting was performed in two stages, the charge being milledprior to the secondary roasting, the results obtained were as shown inTable Xl. In the secondary roasting process each sample of the chargewas exposed to oxygen for the same time as in its primary roastingprocess.

' TABLE XI Total time in Percentage Vanadium oxygen, in min. Extraction5 67.4 10 91.7 20 95.5 30 97.0

The oxidation reaction of fly ash is very much slower than that oftitaniferous magnetite, but when a twostage roasting operation isperformed on the fly ash the results show that vanadium extraction inexcess of 90 percent by weight is obtained for a total exposure time tooxygen of 10 minutes or more.

An investigation of the efi'ect of different particle sizes on theextraction of vanadium was carried out using titaniferous magnetiteground so that all the particles passed through a 60 mesh (B.S.S.)screen. The ore was then dry screened to obtain different particle sizefractions and these fractions were preheated to 800 C. in an inertatmosphere, 28.6 percent by weight of the charge being sodium carbonate,and then exposed to oxygen for 5 minutes. The result obtained for thepercentage vanadium extraction from each fraction is shown in Table XII.

TABLE Xll Approximate Screen fraction Maximum particle Percentage sizein microns Vanadium Extraction 250 52.1 80+l00 177 51.2 l00+l40 149 67.1-l40+200 105 89.7 -200+400 74 92.4 400 37 94.8

Although the above results suggest that it is desirable that the size ofparticles of titaniferous magnetite should be such that they all passthrough a 200 mesh (B.S.S.) screen, it is thought that if the ore wereonly to be ground to pass through a mesh (B.S.S.) screen the percentagevanadium extraction would be acceptable because the presence of aconsiderable amount of finer material promotes the oxidation of coarsermaterial if they are roasted together. Titaniferous magnetite that hasbeen ballmilled can easily be ground to this level.

in the case of fly ash, when similar experiments were performed, the flyash of different particle size fractions being preheated to atemperature of 650 C. in an inert atmosphere, 28.6 percent by weight ofthe charge being sodium carbonate, and then exposed in a layer of 1 cm.in thickness to pure oxygen for 10 minutes, the percentage vanadiumextraction for the plus 100 mesh (B.S.S.) fraction was 95.0 percent byweight and similar high results were obtained for the finer particlefractions. It is therefore concluded that, for the exposure times of 10minutes, changes in the particle size within the range investigated havelittle effect on the percentage vanadium extraction from fly ash.

The effect of different layer thicknesses of charge was investigatedusing titaniferous magnetite that had been ground by the shatter box.The charge, of which 23.05 percent by weight was sodium carbonate, wasspread in a layer over a given area, the layer thickness being increasedby increasing the load per unit area. Layers of 5 mm., 10 mm., l5 mm.,and 20 mm., in thickness were, in turn, preheated in an inert atmosphereto 800 C., the percentage vanadium extraction being detennined fordifferent exposure times for each layer thickness. Although for exposuretimes of 4 minutes and 8 minutes the percentage-extraction increasedslightly as the layer thickness was increased to 15 mm. and thendecreased, the converse was true for exposure times of 16 minutes.Different layer thicknesses within the range of from 5 mm. to 20 mm.appear to have little effect on the extraction of vanadium fromtitaniferous magnetite.

A similar series of experiments but over a wider range of charge layerthicknesses wasperformed on fly ash. For each layer thickness thecharge, 28.6 percent by weight of which was sodium carbonate, waspreheated in an inert atmosphere to 650 C. and then exposed to pureoxygen for 10 minutes. The size of the particles was such that theypassed through a mesh (B.S.S.) screen. The results obtained are shown inTable Xlll below.

TABLE Xlll Layer thickness in Load in g. per Percentage cm. unit areaVanadium Extraction From the above results it can be concluded that asurface loading of 1.5 grams/cm would give high vanadium extraction.Greater loading would make it necessary to have longer exposure times toobtain similar results.

To study the effect of different oxygen concentrations in the atmosphereto which preheated charge is exposed, a series of experiments werecarried out to investigate the effect on the extraction efficiency ofdiluting with nitrogen the oxygen with which preheated slag iscontacted. Thus, samples taken from the same batch of slag werepreheated to the same temperature in an inert atmosphere and were thencontacted, respectively, with an atmosphere consisting (to the extent ofmore than 99% by volume) of oxygen and with atmospheres consisting ofoxygen diluted with different proportions of nitrogen. With all otherrelevant conditions being maintained constant, it was found that theextraction efficiency fell as the proportion of nitrogen increased. Theactual figures are set out in Table XIV herein, in which the percentagesof oxygen and nitrogen are by volume and the extraction efficiency withan atmosphere consisting of oxygen is taken as 100 percent.

TABLE XIV Percentage Percentage of Extraction of oxygen nitrogenefficiency per cent 20 80 30 33 67 30.5 43 57 38.0 50 50 62.2 57 43 86.967 33 90.0 80 20 94.5 99 100.0

It will be seen from Table XIV that the efficiency of the extraction ofvanadium from slag does not fall very rapidly with increasing dilutionof the oxygen until the percentage of oxygen falls to about 60 percentby volume. Thus, while it is preferred to contact the preheated slagwith substantially pure oxygen when that is possible, it is feasible todilute the oxygen a little in order to reduce the maximum temperaturereached by the slag while it is in contact with the oxygen if thatmaximum temperature would otherwise be too high.

A further series of experiments were peformed in which samples oftitaniferous magnetite with which sodium carbonate was incorporated in aquantity equal to 23.1 percent by weight of the total weight of themixture, were preheated to 800 C. in an inert atmosphere.

The samples were then exposed to atmospheres composed of differentproportions of oxygen and nitrogen, each sample being in a layer of 10mm. in thickness and the maximum particle size being 150 microns. After1 minutes, each sample was withdrawn and quenched in water. Theconcentration of oxygen in the gas to which each sample was exposed wasalways in excess of the minimum required for oxidation of the ore, thepartial pressure of the oxygen being varied. For an atmosphere in which10 percent by volume was oxygen, the extent of oxidation was 88.5percent by weight of the total vanadium content. This rose to 94.5percent by weight as the concentration of oxygen was increased to 20percent by volume, and 100 percent by weight for concentrations over 40percent by volume. Oxygen-enriched air would therefore give satisfactoryresults in the extraction of vanadium from titaniferous magnetite.

A similar series of experiments were performed on the fly ash. Samplesof the fly ash, incorporated with sodium carbonate in a quantity equalto 28.6 percent by weight of the total weight of the mixture, werepreheated to 650 C. in an inert atmosphere. The samples were thenexposed to atmospheres of different proportions of oxygen and nitrogenfor 10 minutes in layers of 1 cm. in thickness, the size of theparticles being such that they all passed through a 20 mesh (B.S.S.)screen. When exposed to an atmosphere of pure nitrogen the percentagevanadium extraction, based on the percentage extraction obtained underthe same conditions but using an atmosphere of pure oxygen, was 15.4percent by weight. This value rose to 37.6 percent by weight in anatmosphere in which the proportion of oxygen was 10 percent by volume,69.2 percent by weight as the proportion of oxygen was increased to 20percent by volume and 92.3 percentby weight when the proportion ofoxygen was percent by volume. Thus, in the case of fly ash, a highconcentration (at least in excess of 60 percent by volume) of oxygen inthe atmosphere to which the preheated charge is exposed is desirable forefficient vanadium recovery.

To study the effects of the addition of salts of an alkali metal to thecharge, a number of experiments were carried out to illustrate theeffect of incorporating sodium carbonate with slag prior to contactingthe preheated slag with oxygen. Thus, three slags A, B and C,respectively, were obtained from geographically different sources andtreated in accordance with the invention.

Slag A had the following composition the percentages being by weight andbased on the total weight of the slag:

V,O 30.60% SiO,

14.80% FeO 36.30% MnO 5.18% C50, 6.15% TiO, 5.23% CaO 1.87% MgO 1.66%

solution, the insoluble residues were leached with dilutc sulphuric acidand the vanadium extraction efficiency was determined Sodium carbonatewas incorporated with three of the samples of the slag before preheatingand the results of the experiments, which are set out in Table XVherein, where the percentages of sodium carbonate are by weight andbased on the weight of the mixture of slag and sodium carbonate, showthat the incorporation of sodium carbonate both lowers the maximumtemperature reached by the slag while it is in contact with the oxygenand improves the vanadium extraction efficiency.

TABLE XV Experi- Percentage Preheat Maximum Percentage ment No. ofsodium temperaoxidation vanadium carbonate ture "C temperaextractionture C efficiency Slag B was subjected to four experiments in which theoperating procedures followed exactly those of the experiments carriedout on slag A and the results are set out in Table XVI herein. It willbe seen from Table XVI that, as with slag A, the incorporation of sodiumcarbonate both decreases the maximum temperature reached by the slagwhile it is in contact with the oxygen and increases the vanadiumextraction efficiency. On the other hand, the vanadium extractionefficiency when no sodium carbonate was added is not'as low as with slagA despite the fact that the maximum oxidation temperature was very high.This was because slag B had a much lower vanadium content than slag Aand so was more refractory than slag A, the composition of slag B beingas follows the percentages being by weight and based on the total weightof the slag:

FeO 59.30%

MnO 1.70%

TiO, 0.96%

Cr O, 0.07%

CaO 3.79%

MgO 1.36%

TABLE XVI Experi- Percentage Preheat Maximum Percentage ment No. ofsodium temperaoxidation vanadium carbonate ture C temperaextraction ture"C efficiency 1 0.0 690 1,005 82.15 2 9.1 680 923 88.42 3 13.0 680 88091.20 4 16.7 680 835 94.60

Slag C had the following composition the percentages being by weight andbased on the total weight of the slag:

v,0. 15.00% sio 15.90% CaO 0.37% P 0.06% Fe 39.60% 1 Three samples ofslag C were each mixed with 13.04 percent by weight of sodium carbonate,based on the weight of the mixture, and preheated in an inert atmosphereto different temperatures. Thereafter, the preheated slags were treatedin the same manner as slags A and B were treated, and the results areset out in Table XVII herein. In each of the three experiments that werecarried out on slag C, the maximum temperature reached by the slag whileit was in contact with the oxygen was approximately 260 C. above thepreheat temperature.

TABLE XVII Experi- Preheat Percentage ment No. temperature vanadium "Cextraction efficiency Prior to being treated in accordance with theinvention as described hereinbefore, each of slags A, B and C was groundto 60 mesh (B.S.S.), but the feel test carried out by crumbling the slagin the hand suggested that slag C was the most finely ground and thatslag B was the coarsest.

To study the effects of the addition of salts to anothervanadium-containing material, samples of titaniferous magnetite werefluxed with sodium chloride (that is to say, sodium chloride wasincorporated with the samples) and further samples were fluxed withsodium carbonate, the proportion of fluxing agent in each sample being28.6 percent of the total weight of the sample. The samples were thenroasted in a conventional manner in a muffle furnace at 800 C. It wasfound that, after one hour, the extraction of vanadium from thetitaniferous magnetite fluxed with sodium chloride was 44.4 percent byweight whereas that from the magnetite fluxed with sodium carbonate was77.0 percent by weight. After 2 hours roasting at 800 C. in the mufflefurnace, the values for the extraction of vanadium from two samples oftitaniferous magnetite fluxed with sodium chloride were 33.0 percent and41.6 percent by weight, and those for two samples of the material fluxedwithsodium carbonate were 81.4 percent and 82.9 percent by weight. Thus,fortitaniferous magnetite it is desirable that sodium carbonate shouldbe used as the fluxing agent.

To investigate the effects of different proportions of fluxing agents intitaniferous ore roasted in accordance with the invention, a series ofexperiments were performed on samples of titaniferous magnetite mixedwith different proportions of sodium carbonate. The samples, each beingin a layer of 10 mm. in thickness, were preheated in an inert atmosphereto a temperature of 850 C. and then exposed to pure oxygen for ameasured period of time. The results obtained for-the percentageextraction of vanadium in each case are given in Table XVIII.

TABLE XVIII Percentage Exposure time Percentage concentration to oxygen,in vanadium of fluxing agent minutes extraction 0 10 13.8 1.96 10 81.24.75 15 85.4 7.41 10 97.2 9.1 15 90.4 13.05 15 94.5 13.79 5 96.5 13.7910 97.7 16.65 15 94.4 20.0 15 94.6 23.05 15 97.1 24.25 5 97.0 24.24 1098.0

These results suggest that a concentration in the charge of between 10and 15 percent by weight of sodium carbonate would be adequate for therecovery of over 90 percent by weight of the total vanadium content oftitaniferous magnetite.

Similar series of experiments were performed on samples of fly ash. Thesamples were mixed with different proportions of either sodiumcarbonate, or sodium chloride or sodium sulphate and were roasted in theform of layers of about 1 cm. in thickness for 1 hour at 800 C. in amuffle furnace in a conventional manner not in accordance with theinvention. The samples were then leached using water or an alkalinesolution and the quantity of vanadium recovered was measured. Theresults obtained are given in Table XIX.

TABLE XlX Fluxing Percentage concentration Percentage agent of fluxingagent in Vanadium charge Extraction Na,CO, 0 16.6 9.1 43.6

28.6 82.3 NaCl 0 31.1 9.1 26.3

28.6 3.3 Na SO, 0 35.2 9.1 26.3

From the above results it can be seen that it is desirable to use sodiumcarbonate as the fluxing agent for fly ash. This was found to be themost stable and reliable fluxing agent out of the three with whichexperiments were performed.

To investigate the effects of different proportions of fluxing agent infly ash roasted in accordance with the invention, samples of fly ash,three of which were not mixed with sodium carbonate and the rest ofwhich were mixed with sodium carbonate in proportions ranging from 2.4percent by weight of the charge to 28.6 percent by weight, were eachpreheated in an inert atmosphere to a temperature within the range offrom 600 to 680 C. and then exposed in a layer of 1 cm. in thickness topure oxygen for 10 minutes. The results obtained are given in Table XX.

TABLE XX Proportion of sodium Percentage Vanadium carbonate in charge,Extraction in percent by weight For a percentage extraction of vanadiumof at least percent by weight, the concentration of flux in the chargeshould be in excess of 25 percent by weight of the total weight of thecharge.

In addition to the above experiments a further series of experimentswere performed in which samples of the fly ash, mixed with differentproportions of sodium carbonate, were preheated in an inert atmosphereto a temperature of 680 C. and exposed to oxygen. The samples were thencooled, milled slightly to break down aggregates and re-roasted by againbeing preheated in an inert atmosphere to a temperature of 680 C. andexposed to oxygen. The percentage vanadium extraction obtained onquenching the charge is given in Table XXI.

TABLE XXl Proportion of sodium carbonate in charge, in percent by weight0 Percentage Vanadium Extraction It will be seen that for sodiumcarbonate concentrations of 23.1 percent by weight and over, thepercentage extraction of vanadium from fly ash is higher than thatobtained when it is subjected to only a single roasting operation.

Ferrophosphorus, which generally proves very difficult to process in aconventional manner, was ground in a shatter box and a sample wassubjected to a chemical analysis which showed that it contained 17.78percent by weight of vanadium pentoxide.

To compare the roasting process of the invention with the conventionalroasting process, the ground ferrophosphorus was blended with anhydroussodium carbonate to the extent that the mixture was composed of 23.1percent by weight of sodium carbonate. One sample of the mixture wasthen roasted in a conventional manner in an electric muffle furnace at600 C. for 24 hours and a second sample was preheated to a temperatureof 600 C. in an inert atmosphere and then exposed to an oxygen-richatmosphere for 24 minutes. Both samples were cooled and then leachedwith dilute sulphuric acid solution. The percentage of the totalvanadium content of the charge extracted from the first sample was 34.5percent by weight and from the second sample was 53.7 percent by weight.The conventionally roasted sample was found to have sinteredconsiderably. It was thought that the fact that the extraction ofvanadium was only 53.7 percent from ferrophosphorus roasted inaccordance with the invention, even though this is a considerableimprovement over that obtained from ferrophosphorus when roasted in aconventional manner, was because the ferrophosphorus reacted violentlywith the oxygen after being preheated in an inert atmosphere, a largeliquid phase component being formed.

A series of experiments were performed to determine the effect of mixingwith the ferrophosphorus different proportions of a basic, refractory,phosphorus-and vanadium-containing slag that had been found to reactslowly when exposed to oxygen after being preheated in an inertatmosphere. Such slag had to be preheated to a temperature within therange of from 900 to 950 C. for an acceptable extraction value to beobtained and it was found that the highest'percentage extraction thatcould be obtained was 85 percent to 86 percent by weight. The slag wassubjected to a chemical analysis which showed that it contained 5.99percent by weight of vanadium oxide and about 37 percent by weight ofcalcium and magnesium oxides.

Samples composed of different proportions of ferrophosphorus and basicslag were preheated to 600 C. in an inert atmosphere and then exposed topure oxygen for minutes. The results obtained for the percentagevanadium extraction are shown in Table XXII.

TABLE XXII Proportion Percentof ferro- Proportion of Preheat Time in agephosphorus slag in charge Tempoxygen, extraction in charge in in percentby erature in minof percent by weight in C. utes. Vanadium weight Fromthese results it was deduced that the ferrophosphorus, even when dilutedwith basic slag, still reacts too violently for a high extractionpercentage to be obtained.

In a further series of experiments, the ferrophosphorus was firstroasted in accordance with the invention in the absence of anyadditives, it being preheated in an inert atmosphere to a temperature of600 C. and then exposed to only oxygen-enriched air. The roastedmaterial was cooled down, broken and blended with the basic slag, theproportion of slag in the mixture being 90 percent by weight based onthe total weight of the mixture. Sodium carbonate was then added to themixture in a quantity such that the charge was composed of 28.6 percentby weight of sodium carbonate to control the reaction further and tohelp prevent the formation of liquid phase. Samples, preheated todifferent temperatures in an inert atmosphere, were exposed to oxygenfor 5 minutes. The results obtained for the percentage extraction ofvanadium obtained by acid leaching are shown in Table XXIII.

TABLE XXIII Proportion of Proportion Preheating PercentageFerrophosphorus of slag in temperature Vanadium in mixture in Mixture inin C. Extraction percent by percent by weight weight The extraction ofvanadium from the mixture, when the mixture is preheated to atemperature of at least 650 C. in an inert atmosphere, was greater thanthat obtained from the slag when roasted alone.

The following Example illustrates the invention, the percentages beingby weight:

A slag, which contained 8.3 percent of vanadium, 18.7 percent of SiO and39.3 percent of FeO (the percentages being by weight and based on theweight of the slag) and also chromium, manganese and aluminium, butwhich was low in alkali metals, alkaline earth metals and phosphorus,was ground to 36 mesh (B.S.S.) which corresponds to a maximum particlediameter of approximately 420 microns.

Anhydrous sodium carbonate was blended with the ground slag, theproportions being such that the concentration of anhydrous sodiumcarbonate in the resulting mixture was 28.6 percent by weight.

The mixture was divided into a number of different samples and eachsample was introduced into a flat container to form a layer 1 centimetrethick, and the container was inserted into a tube furnace which waspurged with nitrogen and maintained at a temperature of 680 C. (asindicated by a thermocouple embedded in the sample), the flow ofnitrogen was stopped and replaced by a flow of oxygen. After the oxygenflow had been maintained for a measured time, which was different foreach sample, the oxygen flow was stopped and the flow of nitrogen wasrestarted. The sample was then withdrawn into the cold zone of thefurnace and allowed to cool down.

Each resulting cold sample was slurried with water, stirred, heated to atemperature of approximately C. and filtered. The resulting filtrate andany sample residue were assayed for vanadium and the percentageextraction was calculated using the following formula:

percentage of vanadium extracted vanadium in filtrate (grams) totalvanadium in filtrate and residue (grams) TABLE XXIV Oxygen exposurePercentage extraction time of vanadium nil 2.0 25 sec 50.0 50 sec 80.075 sec 87.0 100 sec 89.0 2.5 min 91.25 3.3'min 9l.25 5.0 min 91.25 6.6min 91.25 8.3 min 91.50 10.0 min 91.75

. I claim:

1. In a process for the beneficiation of a vanadiumcontaining material,wherein the reaction period of vanadium-containing material with oxygenis considerably reduced and at the same timethe percentage extraction ofthe vanadium componentof the material is increased over that obtainedbythe conventional extraction processes used with such materials, thesteps of preheating the material under inert conditions in the absenceof oxygen and free of any reducing effects so as to not effect anychemical change in the material and in the absence of any substance thatwould react to any substantial extent and then contacting the resultinghot material with oxygen to effect the formation of soluble vanadiumcompounds, the preheating of the material being effected to raise thetemperature of the material to such an extent that it is at atemperature of at least 400 C. when it is initially contacted withoxygen and that it reacts with the oxygen in a strongly exothermicmanner, the maximum temperature reached by the material while it is incontact with the oxygen being within the range of from 600 to l,200 C.and below that at which excessive sintering of the material occurs andat which a large liquid-phase component is produced which wouldmaterially reduce extraction efficiency and below the temperature atwhich vanadium metal becomes incandescent the resulting material beingsoluble in aqueous medium.

2. The process of claim 1, wherein the maximum temperature reached bythe slag while it is in contact with the oxygen being within the rangeof from 680 to l,O50 C.

3. The process of claim 2, wherein the maximum temperature reached bythe slag while it is in contact with the oxygen does not exceed 950 C.

4. The process of claim 2, wherein the temperature to which the groundslag is preheated under inert conditions is at least 630 C.

5. The process of claim 1, wherein sodium carbonate is incorporated withthe material prior to its being contacted with oxygen.

6. The process of claim 1, wherein the slag is ground to -36 mesh(B.S.S.), corresponding to a maximum particle diameter of approximately420 microns.

7. The process of claim 1, wherein the vanadiumcontaining material isvanadium-containing titaniferous ore and the temperature to which thematerial is preheated under inert conditions is within the range of from800 to l,000 C.

8. The process of claim 1, wherein the vanadiumcontaining material isfly ash and the temperature to which the material is preheated underinert conditions is within the range of from 400 to 700 C.

9. The process of claim 1, wherein the material is ground to mesh(8.8.8.).

10. The process of claim 1, wherein, after the vanadium-containingmaterial has been contacted with oxygen to effect the formation ofsoluble vanadium compounds, the vanadium-containing material is groundand then reacted with oxygen for a second time at an elevatedtemperature to effect the formation of a further quantity of solublevanadium compounds.

11. The process of claim 10, wherein, after the vanadium-containingmaterial has been ground, it is preheated under inert conditions to atemperature of at least 400 C. prior to its being contacted with oxygenfor a second time the temperature of the preheated material when it isinitially contacted with oxygen for the second time being at least 400C.

12. The process of claim 1, wherein the vanadiumcontaining material isferrophosphorus and, after the ferrophosphorus has been contacted withoxygen to effect the formation of soluble vanadium compounds, it isground, basic vanadium-containing slag is incorporated with it, it ispreheated under inert conditions, and then it is contacted with oxygenfor a second time to ef-= feet the formation of a further quantity ofsoluble vanadium compounds the temperature of the preheated materialwhen it is initially contacted with oxygen for the second time being atleast 400 C.

13. The process of claim 1, wherein, after the material has beencontacted with oxygen for the first time, or, when the material iscontacted with oxygen for a second time, after the material has beencontacted with oxygen for the second time, the material is quenched. =0

2. The process of claim 1, wherein the maximum temperature reached bythe slag while it is in contact with the oxygen being within the rangeof from 680* to 1,050* C.
 3. The process of claim 2, wherein the maximumtemperature reached by the slag while it is in contact with the oxygendoes not exceed 950* C.
 4. The process of claim 2, wherein thetemperature to which the ground slag is preheated under inert conditionsis at least 630* C.
 5. The process of claim 1, wherein sodium carbonateis incorporated with the material prior to its being contacted withoxygen.
 6. The process of claim 1, wherein the slag is ground to -36mesh (B.S.S.), corresponding to a maximum particle diameter ofapproximately 420 micronS.
 7. The process of claim 1, wherein thevanadium-containing material is vanadium-containing titaniferous ore andthe temperature to which the material is preheated under inertconditions is within the range of from 800* to 1,000* C.
 8. The processof claim 1, wherein the vanadium-containing material is fly ash and thetemperature to which the material is preheated under inert conditions iswithin the range of from 400* to 700* C.
 9. The process of claim 1,wherein the material is ground to -100 mesh (B.S.S.).
 10. The process ofclaim 1, wherein, after the vanadium-containing material has beencontacted with oxygen to effect the formation of soluble vanadiumcompounds, the vanadium-containing material is ground and then reactedwith oxygen for a second time at an elevated temperature to effect theformation of a further quantity of soluble vanadium compounds.
 11. Theprocess of claim 10, wherein, after the vanadium-containing material hasbeen ground, it is preheated under inert conditions to a temperature ofat least 400* C. prior to its being contacted with oxygen for a secondtime the temperature of the preheated material when it is initiallycontacted with oxygen for the second time being at least 400* C.
 12. Theprocess of claim 1, wherein the vanadium-containing material isferrophosphorus and, after the ferrophosphorus has been contacted withoxygen to effect the formation of soluble vanadium compounds, it isground, basic vanadium-containing slag is incorporated with it, it ispreheated under inert conditions, and then it is contacted with oxygenfor a second time to effect the formation of a further quantity ofsoluble vanadium compounds the temperature of the preheated materialwhen it is initially contacted with oxygen for the second time being atleast 400* C.
 13. The process of claim 1, wherein, after the materialhas been contacted with oxygen for the first time, or, when the materialis contacted with oxygen for a second time, after the material has beencontacted with oxygen for the second time, the material is quenched.